Ultrasound is commonly known for its uses in non-therapeutic medical procedures, such as tissue imaging for diagnostic purposes. High Intensity Focused Ultrasound (HIFU) is a medical procedure that uses highly focused ultrasound energy to heat and destroy diseased or other unwanted tissue. HIFU systems thereby use ultrasound energy to provide therapeutic benefits in a non-invasive manner. In order to achieve the desired physical effects in the targeted tissue, HIFU involves much higher acoustic intensity levels than diagnostic ultrasound. These high acoustic energy levels are typically obtained by using a transducer that focuses the ultrasound into a focal zone below the skin of the patient being treated. HIFU transducers are therefore typically formed with a spherical shape to provide a nominal focal distance near the middle of a desired range of focal depths. HIFU transducers may also include an array of elements so that the focal distance may be electrically adjusted relative to the nominal focal distance. To treat a desired region of the patient that is larger than the focal zone, the transducer may be moved relative to the region being treated, and/or the focal distance of the transducer adjusted. In this way, the focal zone may be moved to different positions within the desired treatment region until a sufficient dose of HIFU has been delivered.
Thus, there is a need for improved devices, systems, and methods for delivering ultrasound energy to selected regions within a patient using transducers having electrically adjustable focal distances.